THE SYNTHESIS AND NMR STUDY ON THE STABILITY OF DIMETHYLMETHOXOPLATINUM(IV) COMPLEXES | Hadi | Indonesian Journal of Chemistry 21811 40897 1 PB
Indo. J. Chem., 2005, 5 (2), 87 – 91
87
THE SYNTHESIS AND NMR STUDY ON THE STABILITY
OF DIMETHYLMETHOXOPLATINUM(IV) COMPLEXES
Sutopo Hadi*
Chemistry Department, Faculty of Mathematics and Natural Sciences
University of Lampung, Jl. S. Brojonegoro No 1, Gedong Meneng, Bandarlampung 35145 Indonesia
Received 16 April 2005; Accepted 28 April 2005
ABSTRACT
The synthesis of two stable platinum(IV) complexes containing methoxo ligand,
[Pt(CH3)2(OCH3)(OH)py2] (1) and fac-[Pt(CH3)2(OCH3)(H2O)3] (2), has been successfully performed.
Complex 1 was prepared by oxidative addition reaction of cis-[Pt(CH3)2py2] with dry methanol, and a
subsequent reaction of 1 with 70 % HClO4 in water produced the platinum complex 2. The stability of
1
195
complex 2 in acidic aqueous solution was investigated and monitored with H and Pt NMR. The platinum
complex 2 was found to be quite stable toward hydrolysis and no -hydride elimination was observed.
Keywords: Methoxoplatinum(IV), NMR, complex stability, hydrolysis
INTRODUCTION
The preparation of new organoplatinum(II) and
(IV) complexes is still challenging work which is
currently still attracting much attention for platinum
chemist. This is not merely due to their uses as antitumour agent such as in cisplatin complex, cis[Pt(NH3)2Cl2] and its derivatives and some new
class of platinum drugs [1] but they also look closely
at the interesting features of some new class of the
platinum complexes.
The NMR study for two methoxoplatinum(IV),
[Pt(CH3)2(OCH3)(OH)(py)2] (1) and [Pt(CH3)2(OCH3)
+
(H2O)3] (2) has been undertaken to find out and
understand the behaviour of these complexes and
to monitor their stability in acidic solution. This was
performed as it is believed that these
methoxoplatinum(IV) complexes have interesting
and different characteristics to those of platinum(II)
alkoxide in particular or metal alkoxide complexes in
general [2].
Most transition metal methoxo complexes, as
generally known, are susceptible to hydrolysis of
the M-OMe bond to give methanol and/or -hydride
elimination to produce a metal hydride plus
formaldehyde [3]. Complex 2, however, was
prepared in boiling aqueous perchloric acid solution,
and it was stable under the condition used.
Some
other
platinum(IV)
complexes
containing
methoxo
ligand,
such
as
[Pt(CH3)2(OCH3)(OH)(bpy)].H2O
[4]
and
2[Pt(CH3)2(OCH3)(OH)(ox)2] [5] (bpy = 2,2'-bypyridil,
2ox = oxalate), have also been reported as
relatively resistant to the decomposition reaction
* Email address : sutopo_hadi@yahoo.com.au
Sutopo Hadi
that normally occurred in metal alkoxide complexes.
So it would be interesting to have a new class of
metal alkoxide complex which shows different
characteristics to those metal alkoxides in general.
EXPERIMENTAL SECTION
General
1
The H NMR spectra were recorded on a
Bruker AC 200 F spectrometer operating at 200
1
13
15
19
MHz fitted with a 5 mm H, C, N, F Quad
Probe. A spectral width of 2,000 Hz - 2,500 Hz was
employed together with 16 - 96 scans to obtain the
desired F.I.D. A recycle time of 4 s was used with a
pulse width of 3.6 s (thus a tilt angle of 45 degrees
was used). The number of data points obtained was
1
16K. All shifts are positive to higher frequency. H
shifts are relative to the methyl signal of sodium 3trimethylsilylpropane-1-sulfonate (TSS) for aqueous
solvent and to internal tetramethylsilane (TMS) for
non-aqueous solvents.
195
The Pt spectra were recorded at 86.07 MHz
on a Bruker AMX 400 spectro-meter fitted with a 5
mm broadband probe. The magnetisation tilt angle
was 90°. A recycle time of 0.066 s was used with a
pulse width of 23 s. The spectra obtained were
both proton coupled and proton decoupled. A
Spectral width used was 125,000 Hz. The number
of scans used to obtain spectra varied from 1000 to
20,000. The number of data points obtained was
195
16K.
Pt shifts relative to a separate sample
containing an aqueous solution of Na2[PtCl6] (0.5 g
-1
ml ) (Pt = 0).
88
Indo. J. Chem., 2005, 5 (2), 87 – 91
washed with n-hexane and dried in a vacuum
desiccator.
Yield
of
analytically
pure
Pt(CH3)2(OCH3)(OH)(py)2] (1) was 80 %. (Elemental
analysis Found (Calc.) C = 31.3 (31.1); H = 5.8
(5.6); N = 5.7 (5.6)).
Materials
All solvents used were AR Grade. For some
solvents (diethyl ether and methanol) were required
further purification by standard method, for
example, the following procedure has been used to
purify diethyl ether: To 1 L of diethyl ether was
added 200 g of CaCl2 anhydrous, it was kept in the
dark bottle for overnight, mixed with CaH2, and
finally distilled under either high purity grade Argon
or Nitrogen.
Published methods were used to prepare
PtCl2(NBD)
(NBD
=
Norbornadiene
or
bicyclo[2,2,1]hepta-1,3-diene) [6], Pt(CH3)2(NBD)
[7], and cis-Pt(CH3)2py2 (py = pyridine) [8, 9].
+
Preparation of [Pt(CH3)2(OCH3)(H2O)3]
[Pt(CH3)2(OCH3)(OH)(py)2] (1 g, 2.32 mmol)
was suspended in 10 mL of H2O or D2O and 1 mL
of 70 % HClO4 was added. The solid dissolved and
the solution was heated at 80 C for 15 minutes,
and then filtered. The solution contained [Pt(CH3)2
+
+
(OCH3)(H2O)3] as well as pyridinium salt, Hpy .
RESULTS AND DISCUSSION
The
methoxoplatinum(IV)
complex,
[Pt(CH3)2(OCH3)(OH)(py)2] (1) was prepared by
oxidative addition of dry methanol to cis[Pt(CH3)2(py)2] as shown in Fig 1. Rostovtsev et al.
[10] have shown that the reaction of [Pt(CH3)2(N-N)]
(N-N = bpy, phen and tmeda) with methanol always
involves dioxygen. The mechanism of this reaction
is not clear, but they suggested that radical
intermediates are involved. It is likely that the
reaction of cis-[Pt(CH3)2(py)2] with methanol in this
work also involves dioxygen
When the methanol used in this preparation
reaction contains water molecules, without any
further purification, there would be a competition
between small portion water present in methanol
and methanol itself with cis-[Pt(CH3)2(py)2] and this
will lead to a mixture of the product complex 1 and
the possible product [Pt(CH3)2(OH)2(py)2] (3).
Preparation of [Pt(CH3)2(OCH3)(OH)(py)2]
Cis-[Pt(CH3)2(py)2] (1 g, 2.611 mmol) was
dissolved in 40 mL of dry methanol. The solution
was protected from moisture with a drying tube, but
not from air, as it has been shown [10] that the
analogous reaction of [Pt(CH3)2(bpy)] (bpy = 2,2'bypyridil) with methanol proceeds only when
dioxygen is present. The solution was allowed to
stand for 6 hours or more. The solvent was then
removed under high vacuum (reduced pressure) for
3- 4 hours. Further exposure of the sample to high
1
vacuum produced a material whose H NMR
spectrum showed no methoxide peak. The oily
residue was washed successively with small
volume of water, then with acetone, and dried in a
vacuum desiccator over calcium chloride for several
days. The resultant white solid was dissolved in the
minimum
volume of dichloromethane and
reprecipitated by addition of n-hexane, filtered off,
OCH3
H3C
py
Pt
dry MeOH
Pt
H3C
py
H3C
py
H3C
+1
OCH3
70% HClO 4
H3C
OH2
Pt
py
H2O
H3C
OH
OH2
OH2
1
2
long
standing
H3C
py
H3C
py
H3C
H3C
OH
3
Figure 1 The preparative route of complex 1 and 2
Sutopo Hadi
OH2
Pt
Pt
1 +
+2
OH2
OH
OH2
OH2
4
Indo. J. Chem., 2005, 5 (2), 87 – 91
195
The proton decoupled
Pt NMR of 1
shows a singlet peak at –806 p.p.m. relative to
Na2[PtCl6] as external standard. This peak is
similar to that of the product of reaction between
[Pt(CH3)2(bpy)]
and
dry
methanol,
[Pt(CH3)2(OCH3)(OH)(bpy)],
-803
p.p.m.
Preparation of this compound was previous
reported [4]. The complex 2 was obtained by a
subsequent reaction of 1 with water and 70%
perchloric acid and heating at 80 C for 15 minutes.
The amount of perchloric acid used and
temperature control are very important, as they will
affect the platinum product obtained.
1
In the H N.M.R. spectrum of 2 in D2O
solvent, the methyl groups give a singlet with
2
satellites (A, a) at 2.04 p.p.m. and J (Pt – CH3)
75.6 Hz and another singlet with satellites peaks
2
(B, b) from methoxide at 3.2 p.p.m. and J (Pt –
CH3) 30.1 Hz as well as a set of three pyridinium
+
ion peaks, Hpy present in the solution mixture.
Figure 2 (a)) shows the spectrum when the
product 2 was obtained in solution are clearly free
from impurities. The H from proton N.M.R. of 2
1
Figure 1 200.13 MHz H NMR of (a) Freshly and
cleanly prepared of solution 1 (b) Solution
containing 1 with some impurities; Aa = Pt-CH3 in
1, Bb = Pt-OCH3 in 1, C = Set of three pyridinium
+
peaks (Hpy ), D = Impurities, E = Reference (TSS
= sodium-3-trimethylsilylpropane sulfonate)
Sutopo Hadi
89
solution depends on the acidity of the solution used
and the variation value range is about 0.1 - 0.2
p.p.m.
However, in the preparation of 2, there are
often some impurities present as shown in the
proton N.M.R. spectra (an example is in Figure 2
(b)). In Figure 2 (b), the impurity peaks labeled D
correspond to three sets of pyridine peaks and a
singlet with satellites from Pt – CH3.
195
The proton decoupled Pt N.M.R. spectrum of
a solution containing 2 gives a sharp singlet peak at
–556 p.p.m. relative to Na2PtCl6 as an external
standard . The proton coupled spectrum is a simple
septet from Pt – CH3 coupling confirming that the
compound contained two Pt – CH3 groups, the
coupling with the methoxide proton was not
resolved. The Pt is also dependent on the acidity of
solution used in the measu-rement and the
approximate range of this Pt is from -530 to -556
p.p.m. The more acidic the solution used, the more
negative the value (the lower the frequency).
Part of the interest in complex 2 is its high
stability toward both hydrolysis and -hydride
elimination in this acidic aqueous solution. It is,
however, not completely inert towards these
reactions.
Slow hydrolysis occurs when the solution of 2
is left outside on the bench for long periods (2
months or more), but with exposure to normal
laboratories light, no example of -hydride
elimination was observed during the study of this
complex.
The slow hydrolysis of 2 has been monitored
1
mainly with H N.M.R (Figures 2 (a) and (b)) and
195
1
Pt N.M.R (Figure 3). From the H N.M.R.
spectrum, after about three months, another singlet
with satellite in methyl region was observed (G, g
2
label) i.e. at 1.98 p.p.m. and J (Pt – CH3) 75.8 Hz
and this similar to what has been reported by Agnew
9
2
et al. (reported value: H 2.04 p.p.m and J (Pt –
CH3) 75.8 Hz), and this was accompanied by the
appearance of a singlet peak at 3.33 p.p.m which
was assigned free methanol (F). The intensity of
these additional peaks are continued to increase
with time as the solution was left on the bench for
about six months. This free methanol is derived from
the methoxide bound to platinum, which was
displaced by water as in Fig 1.
195
In Pt N.M.R spectra (Figure 4), an additional
peak appears at lower frequency, with Pt value of –
587 p.p.m. (Figure 4 (b)). With time, the intensity of
this additional peak increased and the intensity of
the peaks form the parent compound decreased.
These spectra strengthen the assignment of the new
+
complex was as [Pt(CH3)2(H2O)4] (4) (Pt reported by
Agnew et al. [11], -596 p.p.m.).
90
Indo. J. Chem., 2005, 5 (2), 87 – 91
1
Figure 3 200.13 MHz H NMR of solution 1, (a)
After being left in the bench for about 3 months, (b)
After being left in the bench for about 6 months, Aa
= Pt-CH3 in 1, Bb = Pt-OCH3 in 1, C = Set of three
+
pyridinium peaks (Hpy ), D = Impurities, E =
Reference (TSS = sodium-3-trimethylsilylpropane
sulfonate), F = Free methanol, Gg = Pt-CH3 in 4
Complex
[Pt(CH3)2(OCH3)(OH)(py)2]
(1)
+
[Pt(CH3)2(OCH3)(H2O)3] (2)
[Pt(CH3)2(OH)2(py)2] (3)
2+
[Pt(CH3)2(H2O)4] (4)
a
Not measured
Table 1 NMR data of the platinum(IV) complexes
2
JPt-CH3
Solvent
Pt
H (Me)
(Hz)
p.p.m.
p.p.m.
CDCl3
-806
1.30
73.2
D2O
CDCl3
D2O
-550
a
-587
The NMR data for all complexes observed
presented in this work are tabulated in Table 1.
CONCLUSION
It has been shown that while the Pt – OC3
+
bond in [Pt(CH3)2(OCH3)(H2O)3] (2) is very robust,
hydrolysis does occur over a long period in
aqueous perchloric acid. The reactions of 2 with
halide ions to see the stability Pt – OC3 bond has
been reported previously [12].
Sutopo Hadi
195
Figure 4 86.017 MHz Pt NMR of solution 2 (a) A
freshly prepared; (b) After being left in the bench for
3 months (c) After being left in the bench for 6
months
2.02
1.85
1.98
75.6
71.0
75.8
Other parameters (Hz)
OCH3: H 3.10 (42.4)
OCH3: H 3.20 (30.2)
-
ACKNOWLEDGEMENT
I wish to thank to Prof. T.G. Appleton
(University of Queensland, Brisbane, Australia) for
his valuable help, guidance and discussion. I am
grateful for the award of Scholarship from DUE
Project Universitas Lampung, Indonesia. Thanks
also go to Ms. L. Lambert for her assistance in
N.M.R. experimentation and Dr. G. Ade Ayoko for
his assistance with methyl lithium work.
Indo. J. Chem., 2005, 5 (2), 87 – 91
REFFERENCES
1. Farrel, N.P., 1989, Transition Metal Complexes
as Drugs and Chemotherapeutic Agents,
Kluwer Academic Publihser, Drodrecht, 60
2. Bradley, D.C., Mehrotra R.C., and Gaur, D.P.
1978, Metal Alkoxides.Academic Press,
London, 1
3. Bryndza, H.E. and Tam, W., 1988, Chem.
Rev., 88, 1163
4. Monaghan, P.K. and Puddephatt, R.J., 1984,
Organometallics, 3, 444
5. Dunham, S.O., Larsen, R.D. and Abbot, E.H.,
1993, Inorg. Chem., 32, 2049
6. Drew, D. and Doyle, J.R., 1972, Inorg. Synth.,
13, 48
Sutopo Hadi
91
7. Clark, H.C. and Manzer, L.E., 1973, J.
Organomet. Chem., 59, 411
8. Hadi, S., Appleton, T.G. and Ayoko, G.A., 1998,
st
Proceeding of 1 Brisbane Inorganic Chemistry
Symposium, 13
9. Hadi, S. 2003. Prosiding Seminar Hasil-hasil
Penelitian dan PPM DIES Natalis ke 38
Universitas Lampung, Bandar Lampung, 59
10. Rostovsev, V.V., Labinger, J.A., Bercaw, J.E.,
Lasseter, T.L., and Goldberg, K.I., 1998,
Organometallics, 17, 4530
11. Agnew, N.H., Appleton, T.G. and Hall, J.R.,
1982, Aust. J. Chem., 35, 881
12. Hadi, S., Appleton, T.G. and Ayoko, G.A., 2003,
Inorg. Chim. Acta, 352, 201
87
THE SYNTHESIS AND NMR STUDY ON THE STABILITY
OF DIMETHYLMETHOXOPLATINUM(IV) COMPLEXES
Sutopo Hadi*
Chemistry Department, Faculty of Mathematics and Natural Sciences
University of Lampung, Jl. S. Brojonegoro No 1, Gedong Meneng, Bandarlampung 35145 Indonesia
Received 16 April 2005; Accepted 28 April 2005
ABSTRACT
The synthesis of two stable platinum(IV) complexes containing methoxo ligand,
[Pt(CH3)2(OCH3)(OH)py2] (1) and fac-[Pt(CH3)2(OCH3)(H2O)3] (2), has been successfully performed.
Complex 1 was prepared by oxidative addition reaction of cis-[Pt(CH3)2py2] with dry methanol, and a
subsequent reaction of 1 with 70 % HClO4 in water produced the platinum complex 2. The stability of
1
195
complex 2 in acidic aqueous solution was investigated and monitored with H and Pt NMR. The platinum
complex 2 was found to be quite stable toward hydrolysis and no -hydride elimination was observed.
Keywords: Methoxoplatinum(IV), NMR, complex stability, hydrolysis
INTRODUCTION
The preparation of new organoplatinum(II) and
(IV) complexes is still challenging work which is
currently still attracting much attention for platinum
chemist. This is not merely due to their uses as antitumour agent such as in cisplatin complex, cis[Pt(NH3)2Cl2] and its derivatives and some new
class of platinum drugs [1] but they also look closely
at the interesting features of some new class of the
platinum complexes.
The NMR study for two methoxoplatinum(IV),
[Pt(CH3)2(OCH3)(OH)(py)2] (1) and [Pt(CH3)2(OCH3)
+
(H2O)3] (2) has been undertaken to find out and
understand the behaviour of these complexes and
to monitor their stability in acidic solution. This was
performed as it is believed that these
methoxoplatinum(IV) complexes have interesting
and different characteristics to those of platinum(II)
alkoxide in particular or metal alkoxide complexes in
general [2].
Most transition metal methoxo complexes, as
generally known, are susceptible to hydrolysis of
the M-OMe bond to give methanol and/or -hydride
elimination to produce a metal hydride plus
formaldehyde [3]. Complex 2, however, was
prepared in boiling aqueous perchloric acid solution,
and it was stable under the condition used.
Some
other
platinum(IV)
complexes
containing
methoxo
ligand,
such
as
[Pt(CH3)2(OCH3)(OH)(bpy)].H2O
[4]
and
2[Pt(CH3)2(OCH3)(OH)(ox)2] [5] (bpy = 2,2'-bypyridil,
2ox = oxalate), have also been reported as
relatively resistant to the decomposition reaction
* Email address : sutopo_hadi@yahoo.com.au
Sutopo Hadi
that normally occurred in metal alkoxide complexes.
So it would be interesting to have a new class of
metal alkoxide complex which shows different
characteristics to those metal alkoxides in general.
EXPERIMENTAL SECTION
General
1
The H NMR spectra were recorded on a
Bruker AC 200 F spectrometer operating at 200
1
13
15
19
MHz fitted with a 5 mm H, C, N, F Quad
Probe. A spectral width of 2,000 Hz - 2,500 Hz was
employed together with 16 - 96 scans to obtain the
desired F.I.D. A recycle time of 4 s was used with a
pulse width of 3.6 s (thus a tilt angle of 45 degrees
was used). The number of data points obtained was
1
16K. All shifts are positive to higher frequency. H
shifts are relative to the methyl signal of sodium 3trimethylsilylpropane-1-sulfonate (TSS) for aqueous
solvent and to internal tetramethylsilane (TMS) for
non-aqueous solvents.
195
The Pt spectra were recorded at 86.07 MHz
on a Bruker AMX 400 spectro-meter fitted with a 5
mm broadband probe. The magnetisation tilt angle
was 90°. A recycle time of 0.066 s was used with a
pulse width of 23 s. The spectra obtained were
both proton coupled and proton decoupled. A
Spectral width used was 125,000 Hz. The number
of scans used to obtain spectra varied from 1000 to
20,000. The number of data points obtained was
195
16K.
Pt shifts relative to a separate sample
containing an aqueous solution of Na2[PtCl6] (0.5 g
-1
ml ) (Pt = 0).
88
Indo. J. Chem., 2005, 5 (2), 87 – 91
washed with n-hexane and dried in a vacuum
desiccator.
Yield
of
analytically
pure
Pt(CH3)2(OCH3)(OH)(py)2] (1) was 80 %. (Elemental
analysis Found (Calc.) C = 31.3 (31.1); H = 5.8
(5.6); N = 5.7 (5.6)).
Materials
All solvents used were AR Grade. For some
solvents (diethyl ether and methanol) were required
further purification by standard method, for
example, the following procedure has been used to
purify diethyl ether: To 1 L of diethyl ether was
added 200 g of CaCl2 anhydrous, it was kept in the
dark bottle for overnight, mixed with CaH2, and
finally distilled under either high purity grade Argon
or Nitrogen.
Published methods were used to prepare
PtCl2(NBD)
(NBD
=
Norbornadiene
or
bicyclo[2,2,1]hepta-1,3-diene) [6], Pt(CH3)2(NBD)
[7], and cis-Pt(CH3)2py2 (py = pyridine) [8, 9].
+
Preparation of [Pt(CH3)2(OCH3)(H2O)3]
[Pt(CH3)2(OCH3)(OH)(py)2] (1 g, 2.32 mmol)
was suspended in 10 mL of H2O or D2O and 1 mL
of 70 % HClO4 was added. The solid dissolved and
the solution was heated at 80 C for 15 minutes,
and then filtered. The solution contained [Pt(CH3)2
+
+
(OCH3)(H2O)3] as well as pyridinium salt, Hpy .
RESULTS AND DISCUSSION
The
methoxoplatinum(IV)
complex,
[Pt(CH3)2(OCH3)(OH)(py)2] (1) was prepared by
oxidative addition of dry methanol to cis[Pt(CH3)2(py)2] as shown in Fig 1. Rostovtsev et al.
[10] have shown that the reaction of [Pt(CH3)2(N-N)]
(N-N = bpy, phen and tmeda) with methanol always
involves dioxygen. The mechanism of this reaction
is not clear, but they suggested that radical
intermediates are involved. It is likely that the
reaction of cis-[Pt(CH3)2(py)2] with methanol in this
work also involves dioxygen
When the methanol used in this preparation
reaction contains water molecules, without any
further purification, there would be a competition
between small portion water present in methanol
and methanol itself with cis-[Pt(CH3)2(py)2] and this
will lead to a mixture of the product complex 1 and
the possible product [Pt(CH3)2(OH)2(py)2] (3).
Preparation of [Pt(CH3)2(OCH3)(OH)(py)2]
Cis-[Pt(CH3)2(py)2] (1 g, 2.611 mmol) was
dissolved in 40 mL of dry methanol. The solution
was protected from moisture with a drying tube, but
not from air, as it has been shown [10] that the
analogous reaction of [Pt(CH3)2(bpy)] (bpy = 2,2'bypyridil) with methanol proceeds only when
dioxygen is present. The solution was allowed to
stand for 6 hours or more. The solvent was then
removed under high vacuum (reduced pressure) for
3- 4 hours. Further exposure of the sample to high
1
vacuum produced a material whose H NMR
spectrum showed no methoxide peak. The oily
residue was washed successively with small
volume of water, then with acetone, and dried in a
vacuum desiccator over calcium chloride for several
days. The resultant white solid was dissolved in the
minimum
volume of dichloromethane and
reprecipitated by addition of n-hexane, filtered off,
OCH3
H3C
py
Pt
dry MeOH
Pt
H3C
py
H3C
py
H3C
+1
OCH3
70% HClO 4
H3C
OH2
Pt
py
H2O
H3C
OH
OH2
OH2
1
2
long
standing
H3C
py
H3C
py
H3C
H3C
OH
3
Figure 1 The preparative route of complex 1 and 2
Sutopo Hadi
OH2
Pt
Pt
1 +
+2
OH2
OH
OH2
OH2
4
Indo. J. Chem., 2005, 5 (2), 87 – 91
195
The proton decoupled
Pt NMR of 1
shows a singlet peak at –806 p.p.m. relative to
Na2[PtCl6] as external standard. This peak is
similar to that of the product of reaction between
[Pt(CH3)2(bpy)]
and
dry
methanol,
[Pt(CH3)2(OCH3)(OH)(bpy)],
-803
p.p.m.
Preparation of this compound was previous
reported [4]. The complex 2 was obtained by a
subsequent reaction of 1 with water and 70%
perchloric acid and heating at 80 C for 15 minutes.
The amount of perchloric acid used and
temperature control are very important, as they will
affect the platinum product obtained.
1
In the H N.M.R. spectrum of 2 in D2O
solvent, the methyl groups give a singlet with
2
satellites (A, a) at 2.04 p.p.m. and J (Pt – CH3)
75.6 Hz and another singlet with satellites peaks
2
(B, b) from methoxide at 3.2 p.p.m. and J (Pt –
CH3) 30.1 Hz as well as a set of three pyridinium
+
ion peaks, Hpy present in the solution mixture.
Figure 2 (a)) shows the spectrum when the
product 2 was obtained in solution are clearly free
from impurities. The H from proton N.M.R. of 2
1
Figure 1 200.13 MHz H NMR of (a) Freshly and
cleanly prepared of solution 1 (b) Solution
containing 1 with some impurities; Aa = Pt-CH3 in
1, Bb = Pt-OCH3 in 1, C = Set of three pyridinium
+
peaks (Hpy ), D = Impurities, E = Reference (TSS
= sodium-3-trimethylsilylpropane sulfonate)
Sutopo Hadi
89
solution depends on the acidity of the solution used
and the variation value range is about 0.1 - 0.2
p.p.m.
However, in the preparation of 2, there are
often some impurities present as shown in the
proton N.M.R. spectra (an example is in Figure 2
(b)). In Figure 2 (b), the impurity peaks labeled D
correspond to three sets of pyridine peaks and a
singlet with satellites from Pt – CH3.
195
The proton decoupled Pt N.M.R. spectrum of
a solution containing 2 gives a sharp singlet peak at
–556 p.p.m. relative to Na2PtCl6 as an external
standard . The proton coupled spectrum is a simple
septet from Pt – CH3 coupling confirming that the
compound contained two Pt – CH3 groups, the
coupling with the methoxide proton was not
resolved. The Pt is also dependent on the acidity of
solution used in the measu-rement and the
approximate range of this Pt is from -530 to -556
p.p.m. The more acidic the solution used, the more
negative the value (the lower the frequency).
Part of the interest in complex 2 is its high
stability toward both hydrolysis and -hydride
elimination in this acidic aqueous solution. It is,
however, not completely inert towards these
reactions.
Slow hydrolysis occurs when the solution of 2
is left outside on the bench for long periods (2
months or more), but with exposure to normal
laboratories light, no example of -hydride
elimination was observed during the study of this
complex.
The slow hydrolysis of 2 has been monitored
1
mainly with H N.M.R (Figures 2 (a) and (b)) and
195
1
Pt N.M.R (Figure 3). From the H N.M.R.
spectrum, after about three months, another singlet
with satellite in methyl region was observed (G, g
2
label) i.e. at 1.98 p.p.m. and J (Pt – CH3) 75.8 Hz
and this similar to what has been reported by Agnew
9
2
et al. (reported value: H 2.04 p.p.m and J (Pt –
CH3) 75.8 Hz), and this was accompanied by the
appearance of a singlet peak at 3.33 p.p.m which
was assigned free methanol (F). The intensity of
these additional peaks are continued to increase
with time as the solution was left on the bench for
about six months. This free methanol is derived from
the methoxide bound to platinum, which was
displaced by water as in Fig 1.
195
In Pt N.M.R spectra (Figure 4), an additional
peak appears at lower frequency, with Pt value of –
587 p.p.m. (Figure 4 (b)). With time, the intensity of
this additional peak increased and the intensity of
the peaks form the parent compound decreased.
These spectra strengthen the assignment of the new
+
complex was as [Pt(CH3)2(H2O)4] (4) (Pt reported by
Agnew et al. [11], -596 p.p.m.).
90
Indo. J. Chem., 2005, 5 (2), 87 – 91
1
Figure 3 200.13 MHz H NMR of solution 1, (a)
After being left in the bench for about 3 months, (b)
After being left in the bench for about 6 months, Aa
= Pt-CH3 in 1, Bb = Pt-OCH3 in 1, C = Set of three
+
pyridinium peaks (Hpy ), D = Impurities, E =
Reference (TSS = sodium-3-trimethylsilylpropane
sulfonate), F = Free methanol, Gg = Pt-CH3 in 4
Complex
[Pt(CH3)2(OCH3)(OH)(py)2]
(1)
+
[Pt(CH3)2(OCH3)(H2O)3] (2)
[Pt(CH3)2(OH)2(py)2] (3)
2+
[Pt(CH3)2(H2O)4] (4)
a
Not measured
Table 1 NMR data of the platinum(IV) complexes
2
JPt-CH3
Solvent
Pt
H (Me)
(Hz)
p.p.m.
p.p.m.
CDCl3
-806
1.30
73.2
D2O
CDCl3
D2O
-550
a
-587
The NMR data for all complexes observed
presented in this work are tabulated in Table 1.
CONCLUSION
It has been shown that while the Pt – OC3
+
bond in [Pt(CH3)2(OCH3)(H2O)3] (2) is very robust,
hydrolysis does occur over a long period in
aqueous perchloric acid. The reactions of 2 with
halide ions to see the stability Pt – OC3 bond has
been reported previously [12].
Sutopo Hadi
195
Figure 4 86.017 MHz Pt NMR of solution 2 (a) A
freshly prepared; (b) After being left in the bench for
3 months (c) After being left in the bench for 6
months
2.02
1.85
1.98
75.6
71.0
75.8
Other parameters (Hz)
OCH3: H 3.10 (42.4)
OCH3: H 3.20 (30.2)
-
ACKNOWLEDGEMENT
I wish to thank to Prof. T.G. Appleton
(University of Queensland, Brisbane, Australia) for
his valuable help, guidance and discussion. I am
grateful for the award of Scholarship from DUE
Project Universitas Lampung, Indonesia. Thanks
also go to Ms. L. Lambert for her assistance in
N.M.R. experimentation and Dr. G. Ade Ayoko for
his assistance with methyl lithium work.
Indo. J. Chem., 2005, 5 (2), 87 – 91
REFFERENCES
1. Farrel, N.P., 1989, Transition Metal Complexes
as Drugs and Chemotherapeutic Agents,
Kluwer Academic Publihser, Drodrecht, 60
2. Bradley, D.C., Mehrotra R.C., and Gaur, D.P.
1978, Metal Alkoxides.Academic Press,
London, 1
3. Bryndza, H.E. and Tam, W., 1988, Chem.
Rev., 88, 1163
4. Monaghan, P.K. and Puddephatt, R.J., 1984,
Organometallics, 3, 444
5. Dunham, S.O., Larsen, R.D. and Abbot, E.H.,
1993, Inorg. Chem., 32, 2049
6. Drew, D. and Doyle, J.R., 1972, Inorg. Synth.,
13, 48
Sutopo Hadi
91
7. Clark, H.C. and Manzer, L.E., 1973, J.
Organomet. Chem., 59, 411
8. Hadi, S., Appleton, T.G. and Ayoko, G.A., 1998,
st
Proceeding of 1 Brisbane Inorganic Chemistry
Symposium, 13
9. Hadi, S. 2003. Prosiding Seminar Hasil-hasil
Penelitian dan PPM DIES Natalis ke 38
Universitas Lampung, Bandar Lampung, 59
10. Rostovsev, V.V., Labinger, J.A., Bercaw, J.E.,
Lasseter, T.L., and Goldberg, K.I., 1998,
Organometallics, 17, 4530
11. Agnew, N.H., Appleton, T.G. and Hall, J.R.,
1982, Aust. J. Chem., 35, 881
12. Hadi, S., Appleton, T.G. and Ayoko, G.A., 2003,
Inorg. Chim. Acta, 352, 201